The invention concerns a process for the control of inking in a printing machine, a printing plant suitable for the carrying out of the process and a measuring apparatus for the generation of the control data for such a printing plant.
In continuous printing the control of inking is the most important possibility of affecting the impression of the image. It is performed by visual evaluation or by means of a densitometric analysis of color measuring fields printed with the image. An example of the latter is described in German Patent Publication OS 27 28 738.
It has been discovered in actual practice that the control of inking on the basis of densitometric measurements alone is often insufficient. Thus, it happens frequently that in the case of a setting for equal full-tone densities, appreciable color differences appear between proofs or proof substitutes, respectively, and production runs. These perceived color differences must then be corrected manually by the interactive adjustment of the ink controls. The causes of such differences in printed color may be found in the generally different production processes for proofs/substitute proofs and for production runs and in the color differences of the materials used. Furthermore, in the case of constant ink density printing, and in particular full-tone density printing, constancy of the ink impression is not assured because variations of the tone value occur as the result of soiling of the rubber blanket or of other effects.